In order to understand the mechanism of cell transformation and virus replication in Rous sarcoma virus (RSV) infected cells, various approaches will be made. Characterization of newly isolated ts mutants will be continued. The processing of viral mRNA in infected cells will be studied by the use of microinjection. The packaging of viral mRNA together with virion RNA will be confirmed. A new class of sarcoma virus recovered from tumors induced by transformation defective (td) mutants of RSV will be studies for their RNA structure to establish the origin of RNA sequences acquired. Attempts of translation of viral mRNA isolated from infected cells will be continued.